The present invention relates to rotary drill bits (e.g. twist, spade, etc.) and more particularly to the use of thermally-stable compacts therewith to enable high speed boring of materials.
Heretofore, rotary drills commonly were fabricated from hardened steel. Occasionally, such drills were tipped with tungsten carbide which is a harder material. Later, drill bits fashioned out of tungsten carbide were developed for special applications.
Recently, drill bits have been tipped with superabrasive materials including diamond and cubic boron nitride (CBN). Several methods for tipping drills with superabrasives have been proposed in the art. One proposal is to coat a tungsten carbide drill with a diamond or CBN coating. The usefulness of such coatings has been determined to be dependent at least in part on the thickness of the coating. Fairly thin coatings result in minimal drilling improvement. In the case of ferrous drilling applications, particularly at very high speeds, the reaction of diamond with the ferrous workpiece is a problem. A CBN coating would solve this problem, but no commercial CBN coatings have been available to date.
Another proposal for tipping drills with superabrasives is to add an insert made of the superabrasive to the tip of the drill. One of the major problems in this approach is the attachment of the superabrasive to the slotted tip since CBN and diamond cannot be easily wetted and brazed. This problem, however, typically is solved by making a sandwich of tungsten carbide surmounting the inner core of diamond or CBN. Unfortunately, sandwich compacts necessarily demand larger slots if the same thickness of diamond or CBN layer is to be retained. Larger slots, however, can lead to weakness of the drill tip retaining the sandwich compacts and cannot practically be accommodated by small diameter drill bits.